<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width:300px;
            height: 200px;
            border:1px solid red;
        }
    </style>
</head>
<body>
    <div id="mydiv"></div>
    <input type="text" id="inputMsg">
    <script>
        var inputMsg=document.getElementById("inputMsg");
        var mydiv=document.getElementById("mydiv");

        //元素的值发生改变时触发
        inputMsg.oninput=function(){
            mydiv.innerHTML=this.value;
        };

    </script>
</body>
</html>